Light emitting apparatus, display apparatus, photoelectric conversion apparatus, electric equipment, illumination apparatus, mobile body, wearable device, and image forming apparatus

ABSTRACT

A light emitting apparatus is provided. The light emitting apparatus in which a pixel, that comprises a current path including a light emitting element, a driving transistor configured to supply a current corresponding to a luminance signal to the light emitting element, and a light emission control transistor configured to control light emission or non-light emission of the light emitting element, is arranged. In the current path, the light emission control transistor is arranged between the light emitting element and the driving transistor, and a withstand voltage of the driving transistor is lower than a withstand voltage of the light emission control transistor.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a light emitting apparatus, a displayapparatus, a photoelectric conversion apparatus, an electric equipment,an illumination apparatus, a mobile body, a wearable device, and animage forming apparatus.

Description of the Related Art

A transistor that supplies a current for causing a light emittingelement to emit light with a predetermined luminance needs to be formedby a transistor having a high withstand voltage of about 10 V. Theelement size of a high withstand voltage transistor is larger than theelement size of a low withstand voltage transistor. Accordingly, thechip area of the driving circuit that supplies a current correspondingto the light emission luminance becomes large, and this can cause anincrease in chip cost. Japanese Patent Laid-Open No. 2008-310076describes that a high withstand voltage transistor is arranged between adisplay panel and a driving circuit and the driving circuit is formed bya low withstand voltage transistor.

In a light emitting apparatus such as a display panel which is formed bya plurality of light emitting elements, a luminance variation among thelight emitting elements causes a degradation in image quality. In orderto suppress the degradation in image quality, it is required to decreasethe variation of the driving transistor, which controls the currentflowing in the light emitting element in each pixel, so that thevariation of the current flowing in each light emitting elementdecreases. In the arrangement described in Japanese Patent Laid-Open No.2008-310076, the transistor arranged in the display panel is a highwithstand voltage transistor. Therefore, in order to decrease thevariation of the driving transistor, the area of the high withstandvoltage transistor needs to be increased.

SUMMARY OF THE INVENTION

Each of some embodiments of the present invention has as its object toprovide a technique that suppresses a light emission variation of alight emitting element while suppressing an increase in circuit scale.

According to some embodiments, a light emitting apparatus in which apixel, that comprises a current path including a light emitting element,a driving transistor configured to supply a current corresponding to aluminance signal to the light emitting element, and a light emissioncontrol transistor configured to control light emission or non-lightemission of the light emitting element, is arranged, wherein in thecurrent path, the light emission control transistor is arranged betweenthe light emitting element and the driving transistor, and a withstandvoltage of the driving transistor is lower than a withstand voltage ofthe light emission control transistor, is provided.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments (with reference to theattached drawings).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view showing an arrangement example of a light emittingapparatus of an embodiment;

FIG. 2 is a view showing an arrangement example of a pixel of the lightemitting apparatus shown in FIG. 1 ;

FIG. 3 is a timing chart showing an operation example of the pixel ofthe light emitting apparatus shown in FIG. 1 ;

FIG. 4 is a view showing an arrangement example of a light emissioncontrol transistor arranged in the pixel of the light emitting apparatusshown in FIG. 1 ;

FIG. 5 is a view showing another arrangement example of the lightemitting apparatus of the embodiment;

FIG. 6 is a view showing an arrangement example of a pixel of the lightemitting apparatus shown in FIG. 5 ;

FIGS. 7A to 7C are views showing an example of an image formingapparatus using the light emitting apparatus of the embodiment;

FIG. 8 is a view showing an example of a display apparatus using thelight emitting apparatus of the embodiment;

FIG. 9 is a view showing an example of a photoelectric conversionapparatus using the light emitting apparatus of the embodiment;

FIG. 10 is a view showing an example of an electric equipment using thelight emitting apparatus of the embodiment;

FIGS. 11A and 11B are views each showing an example of a displayapparatus using the light emitting apparatus of the embodiment;

FIG. 12 is a view showing an example of an illumination apparatus usingthe light emitting apparatus of the embodiment;

FIG. 13 is a view showing an example of a mobile body using the lightemitting apparatus of the embodiment; and

FIGS. 14A and 14B are views each showing an example of a wearable deviceusing the light emitting apparatus of the embodiment.

DESCRIPTION OF THE EMBODIMENTS

Hereinafter, embodiments will be described in detail with reference tothe attached drawings. Note, the following embodiments are not intendedto limit the scope of the claimed invention. Multiple features aredescribed in the embodiments, but limitation is not made to an inventionthat requires all such features, and multiple such features may becombined as appropriate. Furthermore, in the attached drawings, the samereference numerals are given to the same or similar configurations, andredundant description thereof is omitted.

With reference to FIGS. 1 to 14B, a light emitting apparatus accordingto an embodiment of the present invention will be described. FIG. 1 is ablock diagram showing the outline of a light emitting apparatus 10 ofthis embodiment. The light emitting apparatus 10 shown in FIG. 1 is alight emitting apparatus in which a light emitting element arranged ineach pixel 101 is driven by a driving circuit which is formed on asemiconductor substrate and corresponds to each light emitting element.The light emitting element can have any material constitution/structureand can use a liquid crystal, an organic light emitting diode (OLED,organic EL), an inorganic LED, or a quantum dot LED. In this embodiment,it will be described that the light emitting apparatus 10 includes,among these light emitting elements, the light emitting element using anorganic EL. As will be described later, in this embodiment, a case willbe described in which a driving transistor for supplying a currentcorresponding to a luminance signal to the light emitting element isconnected to the anode of the organic EL element and all transistors arep-type transistors. However, the present invention is not limited tothis. For example, the polarity and conductivity type of each transistorand those of the semiconductor layer such as a substrate on which thetransistors are formed may all be reversed. Alternatively, for example,the driving transistor may be a p-type transistor and the remainingtransistors may be n-type transistors. Therefore, in the followingdescription, for example, the “drain region” and “source region” of eachtransistor may be reversed appropriately. Potentials to be supplied andthe connection between the components can be changed appropriately inaccordance with the polarities and conductivity types of the componentsof the light emitting apparatus 10.

As shown in FIG. 1 , the light emitting apparatus 10 includes a pixelarray 100 and a driving unit arranged in the periphery of the pixelarray 100. A plurality of the pixels 101 two-dimensionally arranged in amatrix are arranged in the pixel array 100, and a light emitting element110 (shown in FIG. 2 ) is arranged in each pixel 101. The light emittingelement 110 of each pixel 101 emits light with a light emission amountcorresponding to an input signal voltage.

The driving unit is a circuit for driving each pixel 101. The drivingunit includes, for example, a light emission control circuit 200 and asignal output circuit 300. In the pixel array 100, a light emissioncontrol line 210 and a signal line 310 are arranged along the columndirection for each pixel column.

The light emission control circuit 200 outputs, via the light emissioncontrol line 210, a light emission control signal for controlling lightemission or non-light emission of each pixel 101. The signal outputcircuit 300 outputs, via the signal line 310, a luminance signal (signalvoltage) for controlling the luminance of each pixel 101. The lightemission control line 210 may be formed by a plurality of control linesfor each pixel column.

For example, for each column, the light emission control line 210 may beformed by the control lines, the number of which corresponds to thenumber of pixel rows, and each control line may be connected to eachpixel 101 in a one-to-one relationship. In this case, the pixel array100 can be configured to be capable of controlling the number of lightemitting pixels for each pixel column.

FIG. 2 is a circuit diagram showing an arrangement example of the pixel101 arranged in the pixel array 100. As shown in FIG. 2 , each of theplurality of pixels 101 includes a current path including the lightemitting element 110, a driving transistor 112 for supplying a currentcorresponding to a luminance signal to the light emitting element 110,and a light emission control transistor 111 for controlling lightemission or non-light emission of the light emitting element 110. Here,the total number of transistors arranged in the pixel 101 and thecombination of the conductivity types of the transistors are merelyexamples, and they are not limited to this arrangement.

In the arrangement shown in FIG. 2 , one main terminal (the drain inthis embodiment) of the main terminals of the light emission controltransistor 111 is connected to one main terminal of the light emittingelement 110, and the connection point is referred to as a node 220. Theother main terminal (the source in this embodiment) of the mainterminals of the light emission control transistor 111 is connected toone main terminal (the drain in this embodiment) of the drivingtransistor 112, and the connection point is referred to as a node 221.The other main terminal (the source in this embodiment) of the drivingtransistor 112 is connected to a power supply voltage Vdd. The othermain terminal of the light emitting element 110 is connected to a powersupply voltage Vss. The control terminal (gate) of the light emissioncontrol transistor 111 is connected to the light emission control line210. The control terminal (gate) of the driving transistor 112 isconnected to the signal line 310.

The driving transistor 112 supplies a driving current, which correspondsto the signal voltage of the luminance signal supplied from the signaloutput circuit 300 via the signal line 310, from the power supplyvoltage Vdd to the light emission control transistor 111. The lightemission control transistor 111 is controlled between a conductive stateand a non-conductive state by a light emission control signal outputfrom the light emission control circuit 200 via the light emissioncontrol line 210. When the light emission control transistor 111 is setin the conductive state in accordance with the light emission controlsignal, the driving current is supplied from the driving transistor 112to the light emitting element 110. Thus, the light emitting element 110emits light.

At this time, the light emission luminance of the light emitting element110 changes in accordance with the driving current supplied from thedriving transistor 112 and flowing in the current path including thelight emitting element 110, the driving transistor 112, and the lightemission control transistor 111. In the pixel array 100, when causingthe light emitting element 110 arranged in each pixel 101 to emit lightat a constant luminance, the signal output circuit 300 outputs, as aluminance signal, a constant voltage to the control terminal of eachdriving transistor 112 via each signal line 310. However, since therecan be a variation of the characteristic such as a variation of athreshold voltage Vth among the driving transistors 112, even if thesame voltage is supplied to the control terminals, the driving currentsupplied to the light emitting element 110 may vary among the pixels101. It is known that, in general, the magnitude of the variation of thecharacteristic among the transistors is inversely proportional to thesquare root of the gate area of the transistor and proportional to thegate film thickness. Accordingly, in order to suppress the variation ofthe characteristic among the transistors, it is effective to increasethe gate area and decrease the gate film thickness.

On the other hand, when causing the light emitting operation of thelight emitting element 110 at a predetermined luminance, a forwardvoltage Vf of several V is required. Therefore, a voltage of about 10 Vmay be required between the power supply voltage Vdd and the powersupply voltage Vss of the pixel 101. In general, a high withstandvoltage transistor having a withstand voltage of about 10 V has a largergate film thickness than a low withstand voltage transistor with a lowerwithstand voltage, or has a larger element area because it has aspecific structure. Hence, the high withstand voltage transistor has alarger characteristic variation and a larger element area than the lowerwithstand voltage transistor.

In this embodiment, the driving transistor 112 is a low withstandvoltage transistor, and has a lower withstand voltage than the lightemission control transistor 111 which uses a high withstand voltagetransistor. The light emission control transistor 111 is only requiredto perform a switching operation to control light emission or non-lightemission of the light emitting element 110, so it does not largelycontribute to the variation of the driving current. Therefore, althoughthe light emission control transistor 111 uses a high withstand voltagetransistor, it does not require a larger area than the drivingtransistor 112 having a low withstand voltage.

FIG. 3 is a timing chart illustrating an operation of the pixel 101shown in FIG. 2 . Each of a period from time t0 to time t1 and a periodfrom time t2 to time t3 represents a non-light emission period of thelight emitting element 110. A period from time t1 to time t2 representsa light emission period of the light emitting element 110. In a periodfrom time t0 to time t3, the driving transistor 112 is constantly activeand supplies the signal voltage of a luminance signal for causing thelight emitting element 110 to emit light at a predetermined luminance.

In the non-light emission period from time t0 to time t1, the lightemission control signal supplied to the light emission control line 210becomes a voltage close to the power supply voltage Vdd, so that thelight emission control transistor 111 is turned off and set in thenon-conductive state. In this case, the potential of the node 220corresponding to the drain of the light emission control transistor 111is decreased to the potential close to the power supply voltage Vss bythe forward current generated in the light emitting element 110.Further, the potential of the node 221 corresponding to the drain of thedriving transistor 112 is increased to the potential close to the powersupply voltage Vdd by the driving transistor 112.

Then, in the light emission period from time t1 to time t2, thepotential of the light emission control signal is decreased to thepotential exceeding the threshold voltage of the light emission controltransistor 111 so that the light emission control transistor 111 is setin the conductive state. Accordingly, the potential of each of the node220 and the node 221 becomes close to the potential (to be referred toas a voltage Von hereinafter) obtained by adding the forward voltage Vfof the light emitting element 110 to the power supply voltage Vss,thereby causing the light emitting operation of the light emittingelement 110.

In the operation described above, for the light emission controltransistor 111, a potential difference corresponding to the differencebetween the power supply voltage Vdd and the power supply voltage Vss isgenerated between the gate and drain and between the drain and source inthe non-light emission period. Therefore, it requires a high withstandvoltage. On the other hand, for the driving transistor 112, a potentialdifference corresponding to difference between the power supply voltageVdd and the power supply voltage Vss is not generated between the gateand the drain and between the drain and the source in the non-lightemission period and the light emission period. Accordingly, it can befound that it does not require a high withstand voltage. That is, in thecurrent path of the pixel 101 including the light emitting element 110,the driving transistor 112, and the light emission control transistor111, the light emission control transistor 111 is arranged between thelight emitting element 110 and the driving transistor 112. With thisarrangement, the driving transistor 112 can have the withstand voltagelower than the withstand voltage of the light emission controltransistor 111. Thus, the low withstand voltage transistor having asmaller characteristic variation and a smaller element area than thehigh withstand voltage transistor can be used as the driving transistor112 that controls the current flowing through the light emitting element110 arranged in the pixel 101. That is, it is possible to suppress thelight emission variation of the light emitting element 110 whilesuppressing an increase in circuit scale.

In addition, when causing the light emitting operation of the lightemitting element 110, a potential difference is generated due to theon-resistance of the light emission control transistor 111. Thus, thepotential of the light emission control line 210 becomes slightly lowerthan the potential of the node 221. Here, the potential of the lightemission control line 210 is only required to exceed the thresholdvoltage of the light emission control transistor 111, and does not haveto decrease to the potential of the power supply voltage Vss.Accordingly, the light emission control circuit 200 that supplies, tothe control terminal of the light emission control transistor 111, thelight emission control signal for controlling light emission ornon-light emission of the light emitting element 110 does not need ahigh withstand voltage. Therefore, the withstand voltage of thetransistor arranged in the light emission control circuit 200 may belower than the withstand voltage of the light emission controltransistor 111.

For example, the difference between the withstand voltage of the drivingtransistor 112 and the withstand voltage of the transistor arranged inthe light emission control circuit 200 may be smaller than thedifference between the withstand voltage of the driving transistor 112and the withstand voltage of the light emission control transistor 111.Further, for example, the withstand voltage of the driving transistor112 may be equal to the withstand voltage of the transistor arranged inthe light emission control circuit 200. In this case, the gate area andgate film thickness of the driving transistor 112 may be equal to thoseof the transistor arranged in the light emission control circuit 200.When the light emission control circuit 200 includes the arrangement asdescribed above, the circuit scale of the light emission control circuit200 can be decreased.

FIG. 4 is a schematic view showing an example of the arrangement of thelight emission control transistor 111 which is the transistor having ahigh withstand voltage. Here, a high withstand voltage transistor havinga p-type LOCOS offset structure is formed on an n-type semiconductorsubstrate (for example, a silicon substrate). A p⁻-type well region 502and an n-type well region 503 are formed in the upper surface of ann⁻-type semiconductor substrate 501. A p⁺-type drain region 504 isformed in a part of the surface of the well region 502, and a p⁺-typesource region 505 is formed in a part of the surface of the well region503. A gate insulation film 506 (for example, silicon oxide) is formedon the entire surface of the semiconductor substrate 501, and a LOCOS isformed in the part of a region 507 on the well region 502. A gateelectrode 509 is formed on the gate insulation film 506 on the wellregion 502 and the well region 503.

With the LOCOS offset structure as described above, the light emissioncontrol transistor 111 can have a high withstand voltage between thegate and the drain and between the drain and the source. Further, boththe normal driving transistor 112 (low withstand voltage transistor), inwhich the gate electrode and the drain are not offset (the gateelectrode is arranged on a part of the drain), and the light emissioncontrol transistor 111 as the high withstand voltage transistor can beimplemented without largely increasing the number of steps of themanufacturing process.

Further, since a large gate voltage is not required to cause theswitching operation of the light emission control transistor 111, as hasbeen described above, the light emission control circuit 200 thatsupplies the light emission control signal can be formed by the lowwithstand voltage transistor alone. Similarly, the signal output circuit300 for supplying a luminance signal to the control terminal of thedriving transistor 112 having a low withstand voltage does not require ahigh withstand voltage. Therefore, the withstand voltage of thetransistor arranged in the signal output circuit 300 may be lower thanthe withstand voltage of the light emission control transistor 111.

For example, the difference between the withstand voltage of the drivingtransistor 112 and the withstand voltage of the transistor arranged inthe signal output circuit 300 may be smaller than the difference betweenthe withstand voltage of the driving transistor 112 and the withstandvoltage of the light emission control transistor 111. Further, forexample, the withstand of the driving transistor 112 may be equal to thewithstand voltage of the transistor arranged in the signal outputcircuit 300. In this case, the gate area and gate film thickness of thedriving transistor 112 may be equal to those of the transistor arrangedin the signal output circuit 300. When the signal output circuit 300 hasthe arrangement as described above, the circuit scale of the signaloutput circuit 300 can be decreased.

The light emission control transistor 111 is only required to be atransistor having a high withstand voltage, and is not limited to aLOCOS offset transistor. For example, the light emission controltransistor 111 may be a transistor having a drain offset structure inwhich the gate electrode and the drain are offset so as not to overlapeach other by the STI structure or the like.

With the arrangement described in this embodiment, it is possible toimplement the light emitting apparatus 10 in which the light emissionvariation of the light emitting element 110 is suppressed whilesuppressing an increase in circuit area of the pixel array 100 in whichthe pixels 101 are arranged. It is also possible to suppress the circuitarea of each of the light emission control circuit 200 and the signaloutput circuit 300.

With reference FIGS. 5 and 6 , a modification of the light emittingapparatus 10 described above will be described. In this embodiment, inorder to further suppress the variation of the driving current in thepixel 101, the pixel 101 is formed by a cascode circuit. FIG. 5 is ablock diagram showing a modification of the light emitting apparatus 10shown in FIG. 1 . As shown in FIG. 5 , in the pixel array 100, a biasline 311 is arranged along the column direction for each pixel column.The bias line 311 is connected to the output end of the correspondingcolumn in the signal output circuit 300, and supplies a bias signal tothe pixel 101. The signal output circuit 300 can include a bias circuit320 that generates a bias signal. In the arrangement shown in FIG. 5 ,the bias circuit 320 is arranged in the signal output circuit 300, butthe present invention is not limited to this. The signal output circuit300 and the bias circuit 320 may be arranged as independent circuits.

FIG. 6 is a circuit diagram showing an arrangement example of the pixel101 arranged in the light emitting apparatus 10 shown in FIG. 5 . Asshown in FIG. 6 , in the current path in which the driving current ofthe light emitting element 110 flows, a cascode transistor 113 forcontrolling the potential of the drain of the driving transistor 112 isarranged between the driving transistor 112 and the light emissioncontrol transistor 111.

More specifically, one main terminal (the drain in this embodiment) ofthe main terminals of the cascode transistor 113 is connected to onemain terminal (the source in this embodiment) of the main terminals ofthe light emission control transistor 111, and the connection point isreferred to as a node 222. The other main terminal of the cascodetransistor 113 (the source in this embodiment) is connected to one mainterminal (the drain in this embodiment) of the main terminals of thedriving transistor 112, and the connection point is referred to as anode 223. The control terminal (gate) of the cascode transistor 113 isconnected to the bias line 311, and receives the signal voltage of thebias signal supplied from the bias circuit of the signal output circuit300.

In the pixel array 100, when causing the respective light emittingelements 110 to emit light at a constant luminance, the forward voltageVf of several V is required. However, it is conceivable that the forwardvoltage Vf varies due to the characteristic variation of the lightemitting element 110. If the forward voltage Vf varies, the potential ofthe node 220 corresponding to the drain potential of the light emissioncontrol transistor 111 varies. Thus, when the light emission controltransistor 111 is turned on and set in the conductive state, thepotential of the node 222 similarly varies. Further, when the drivingcurrent is large, the voltage drop caused by the power supply wiringimpedance of the power supply voltage Vss cannot be ignored, and alarger variation may be superimposed on the above-described variation.

On the other hand, in the pixel 101 shown in FIG. 6 , the drivingtransistor 112 and the cascode transistor 113 form a cascode circuit.Therefore, even if the potential of each of the node 220 and the node222 varies, the cascode transistor 113 receiving the bias signal fromthe bias line 311 controls the potential of the node 223 correspondingto the drain potential of the driving transistor 112 to near apredetermined potential. Accordingly, even if the potential of the node220 varies for each light emitting element 110, the driving currentoutput from the driving transistor 112 can be kept constant.

Similar to the driving transistor 112, in the cascode transistor 113, apotential difference corresponding to the difference between the powersupply voltage Vdd and the power supply voltage Vss is not generatedbetween the gate and the drain and between the drain and source.Accordingly, it does not require a high withstand voltage. Therefore,the withstand voltage of the cascode transistor 113 may be lower thanthe withstand voltage of the light emission control transistor 111. Forexample, the difference between the withstand voltage of the drivingtransistor 112 and the withstand voltage of the cascode transistor 113may be smaller than the difference between the withstand voltage of thedriving transistor 112 and the withstand voltage of the light emissioncontrol transistor 111. Further, for example, the withstand voltage ofthe driving transistor 112 may be equal to the withstand voltage of thecascode transistor 113. In this case, the gate area and gate filmthickness of the driving transistor 112 may be equal to those of thecascode transistor 113.

In addition, the bias circuit 320 of the signal output circuit 300 thatsupplies the bias signal to the control terminal of the cascodetransistor 113 having a low withstand voltage does not require a highwithstand voltage. Accordingly, the withstand voltage of the transistorarranged in the bias circuit 320 may be lower than the withstand voltageof the light emission control transistor 111. For example, thedifference between the withstand voltage of the driving transistor 112and the withstand voltage of the transistor arranged in the bias circuit320 may be smaller than the difference between the withstand voltage ofthe driving transistor 112 and the withstand voltage of the lightemission control transistor 111. Further, for example, the withstandvoltage of the driving transistor 112 may be equal to the withstandvoltage of the transistor arranged in the bias circuit 320. In thiscase, the gate area and gate film thickness of the driving transistor112 may be equal to those of the transistor arranged in the bias circuit320. When the bias circuit 320 has the arrangement as described above,the circuit scale of the bias circuit 320 can be decreased.

With the arrangement shown in FIGS. 5 and 6 , it is possible toimplement the light emitting apparatus 10 in which the light emissionvariation of the light emitting element 110 is suppressed whilesuppressing an increase in circuit area of the pixel array 100 in whichthe pixels 101 are arranged. It is also possible to suppress the circuitarea of each of the light emission control circuit 200, the signaloutput circuit 300, and the bias circuit 320. For example, the withstandvoltage of the light emission control transistor 111 arranged in eachpixel 101 may be the highest among the transistors included in the lightemitting apparatus 10. By limiting the use of a large transistor havinga high withstand voltage to the light emission control transistor 111,it is possible to implement the light emitting apparatus 10 in which thelight emission variation of the light emitting element 110 is suppressedwhile suppressing the circuit scale.

Here, application examples in which the light emitting apparatus 10 ofthis embodiment is applied to an image forming apparatus, a displayapparatus, a photoelectric conversion apparatus, an electronicequipment, an illumination apparatus, a mobile body, and a wearabledevice will be described with reference to FIGS. 7A to 14B. In addition,the light emitting apparatus 10 is applicable to the exposure lightsource of an electrophotographic image forming apparatus, the backlightof a liquid crystal display apparatus, a light emitting device includinga color filter in a white light source, and the like. The displayapparatus may be an image information processing apparatus that includesan image input unit for inputting image information from an area CCD, alinear CCD, a memory card, or the like, and an information processingunit for processing the input information, and displays the input imageon a display unit. In addition, a display unit included in a camera oran inkjet printer may have a touch panel function. The driving type ofthe touch panel function may be an infrared type, a capacitance type, aresistive film type, or an electromagnetic induction type, and is notparticularly limited. The display apparatus may be used for the displayunit of a multifunction printer.

FIGS. 7A to 7C are schematic views showing an example of an imageforming apparatus using the light emitting apparatus 10 of thisembodiment. An image forming apparatus 926 shown in FIG. 7A includes aphotosensitive member 927, an exposure light source 928, a developingunit 931, a charging unit 930, a transfer device 932, a conveyance unit933 (a conveyance roller in the arrangement shown in FIG. 7A), and afixing device 935.

Light 929 is emitted from the exposure light source 928, and anelectrostatic latent image is formed on the surface of thephotosensitive member 927. The light emitting apparatus 10 including theabove-described light emitting element 110 can be applied to theexposure light source 928. The developing unit 931 can function as adeveloping device that contains a toner or the like as a developingagent and applies the developing agent to the exposed photosensitivemember 927. The charging unit 930 charges the photosensitive member 927.The transfer device 932 transfers the developed image to a print medium934. The conveyance unit 933 conveys the print medium 934. The printmedium 934 can be, for example, paper or a film. The fixing device 935fixes the image formed on the print medium.

Each of FIGS. 7B and 7C is a schematic view showing a plurality of lightemitting units 936 arranged along the longitudinal direction on a longsubstrate in the exposure light source 928. The light emitting apparatus10 including the above-described light emitting element 110 can beapplied to each of the light emitting units 936. A direction 937 is adirection parallel to the axis of the photosensitive member 927, andrepresents the column direction in which the pixels 101 are arrayed inthe pixel array 100 of the light emitting apparatus 10. This columndirection matches the direction of the axis upon rotating thephotosensitive member 927. This direction 937 can be referred to as thelong-axis direction of the photosensitive member 927.

FIG. 7B shows a form in which the light emitting units 936 are arrangedalong the long-axis direction of the photosensitive member 927.

FIG. 7C shows a form, which is a modification of the arrangement of thelight emitting units 936 shown in FIG. 7B, in which the light emittingunits 936 are arranged in the column direction alternately between thefirst column and the second column. The light emitting units 936 arearranged at different positions in the row direction between the firstcolumn and the second column. In the first column, multiple lightemitting units 936 are arranged spaced apart from each other. In thesecond column, the light emitting unit 936 is arranged at the positioncorresponding to the space between the light emitting units 936 in thefirst column. Also in the row direction, multiple light emitting units936 are arranged spaced apart from each other. The arrangement of thelight emitting units 936 shown in FIG. 7C can be referred to as, forexample, an arrangement in a grid pattern, an arrangement in a staggeredpattern, or an arrangement in a checkered pattern.

FIG. 8 is a schematic view showing an example of a display apparatususing the light emitting apparatus 10 of this embodiment. A displayapparatus 1000 may include, between an upper cover 1001 and a lowercover 1009, a touch panel 1003, a display panel 1005, a frame 1006, acircuit board 1007, and a battery 1008. The touch panel 1003 and thedisplay panel 1005 are connected to flexible printed circuit FPCs 1002and 1004, respectively. Active elements such as transistors are arrangedon the circuit board 1007. The battery 1008 need not be provided if thedisplay apparatus 1000 is not a portable device, and need not beprovided in this position even if the display apparatus is a portabledevice. The above-described light emitting apparatus 10 can be appliedto the display panel 1005. The light emitting apparatus 10 functioningas the display panel 1005 is connected to the active element such as thetransistor arranged on the circuit board 1007 to be operated.

The display apparatus 1000 shown in FIG. 8 may be used for the displayunit of a photoelectric conversion apparatus (image capturing apparatus)that includes an optical unit including a plurality of lenses and animage sensor that receives light having passed through the optical unitand photoelectrically converts the light into an electric signal. Thephotoelectric conversion apparatus may include a display unit whichdisplays information acquired by the image sensor. The display unit maybe a display unit exposed to the outside of the photoelectric conversionapparatus, or a display unit arranged in a viewfinder. The photoelectricconversion apparatus may be a digital camera or a digital video camera.

FIG. 9 is a schematic view showing an example of a photoelectricconversion apparatus using the light emitting apparatus 10 of thisembodiment.

A photoelectric conversion apparatus 1100 may include a viewfinder 1101,a rear display 1102, an operation unit 1103, and a housing 1104. Thephotoelectric conversion apparatus 1100 can be referred to as an imagecapturing apparatus. The light emitting apparatus 10 described above canbe applied to the viewfinder 1101 serving as the display unit. In thiscase, the light emitting apparatus 10 may display not only an image tobe captured, but also environment information, an image capturinginstruction, and the like. The environment information may include theintensity of ambient light, the direction of ambient light, the movingspeed of an object, the possibility that the object is blocked by ashielding object, or the like.

Since the timing suitable for capturing an image is often a short time,it is better to display the information as quickly as possible.Therefore, the light emitting apparatus 10 including an organic lightemitting material such as an organic EL element as the light emittingelement 110 can be used in the viewfinder 1101. This is because theorganic light emitting material has a high response speed. The lightemitting apparatus 10 using the organic light emitting material is moresuitably than a liquid crystal display apparatus in the apparatuses thatrequire a high display speed.

The photoelectric conversion apparatus 1100 includes an optical unit(not shown). The optical unit includes a plurality of lenses and formsan image on a photoelectric conversion element (not shown), whichreceives light having passed through the optical unit, housed in thehousing 1104. It is possible to adjust the focus by adjusting therelative positions of the plurality of lenses. This operation can beperformed automatically.

The light emitting apparatus 10 may be applied to the display unit of anelectronic equipment. In this case, the display unit may have both adisplay function and an operation function. Examples of the mobileterminal include a mobile phone such as a smartphone, a tablet, and ahead mounted display.

FIG. 10 is a schematic view showing an example of an electronicequipment using the light emitting apparatus 10 of this embodiment. Anelectronic equipment 1200 includes a display unit 1201, an operationunit 1202, and a housing 1203. The housing 1203 may include a circuit, aprinted board including the circuit, a battery, and a communicationunit. The operation unit 1202 may be a button or a touch panel typesensing unit. The operation unit 1202 may be a biometrics unit thatrecognizes a fingerprint and releases a lock or the like. A portabledevice including a communication unit can also be called a communicationequipment. The above-described light emitting apparatus 10 can beapplied to the display unit 1201.

FIGS. 11A and 11B are schematic views showing examples of a displayapparatus using the light emitting apparatus 10 of this embodiment. FIG.11A shows a display apparatus such as a television monitor or a PCmonitor. A display apparatus 1300 includes a frame 1301 and a displayunit 1302. The above-described light emitting apparatus 10 can beapplied to the display unit 1302. The display apparatus 1300 may includea base 1303 that supports the frame 1301 and the display unit 1302. Thebase 1303 is not limited to the form shown in FIG. 11A. For example, thelower side of the frame 1301 may serve as the base 1303. The frame 1301and the display unit 1302 may be bent. The curvature radius may bebetween 5,000 mm (inclusive) and 6,000 mm (inclusive).

FIG. 11B is a schematic view showing another example of the displayapparatus using the light emitting apparatus 10 of this embodiment. Adisplay apparatus 1310 shown in FIG. 11B is configured to be bendable,and is a so-called foldable display apparatus. The display apparatus1310 includes a first display unit 1311, a second display unit 1312, ahousing 1313, and a bending point 1314. The above-described lightemitting apparatus 10 can be applied to each of the first display unit1311 and the second display unit 1312. The first display unit 1311 andthe second display unit 1312 may be one seamless display apparatus. Thefirst display unit 1311 and the second display unit 1312 can be dividedat the bending point. The first display unit 1311 and the second displayunit 1312 may display different images, or one image may be displayedwith the first display unit and the second display unit.

FIG. 12 is a schematic view showing an example of an illuminationapparatus using the light emitting apparatus 10 of this embodiment. Anillumination apparatus 1400 may include a housing 1401, a light source1402, a circuit board 1403, an optical film 1404, and a light diffusionunit 1405. The above-described light emitting apparatus 10 can beapplied to the light source 1402. The optical film 1404 may be a filterthat improves the color rendering property of the light source. Thelight diffusion unit 1405 can effectively diffuse light from the lightsource to illuminate a wide range for lighting up or the like. A covermay be provided in the outermost portion, as needed. The illuminationapparatus 1400 may include both the optical film 1404 and the lightdiffusion unit 1405, or may include only one of them.

The illumination apparatus 1400 is, for example, an apparatus thatilluminates a room. The illumination apparatus 1400 may emit light ofwhite, day white, or any other color from blue to red. The illuminationapparatus 1400 may include a light control circuit for controlling thelight color. The illumination apparatus 1400 may include a power supplycircuit connected to the light emitting apparatus 10 which functions asthe light source 1402. The power supply circuit is a circuit thatconverts an AC voltage into a DC voltage. Note that white light has acolor temperature of 4200K, and day-white light has a color temperatureof 5000K. The illumination apparatus 1400 may also include a colorfilter. Further, the illumination apparatus 1400 may include a heatdissipation portion. The heat dissipation portion releases the heat inthe apparatus to the outside of the apparatus, and examples thereofinclude a metal having high specific heat, liquid silicon, and the like.

FIG. 13 is a schematic view showing an automobile including a tail lampwhich is an example of the lighting unit for an automobile using thelight emitting apparatus 10 of this embodiment. An automobile 1500includes a tail lamp 1501, and may turn on the tail lamp 1501 when abrake operation or the like is performed. The light emitting apparatus10 of this embodiment may be used in a head lamp as the lighting unitfor an automobile. The automobile is an example of a mobile body, andthe mobile body may be a ship, a drone, an aircraft, a railroad car, anindustrial robot, or the like. The mobile body may include a body and alighting unit provided in the body. The lighting unit may inform thecurrent position of the body.

The above-described light emitting apparatus 10 can be applied to thetail lamp 1501. The tail lamp 1501 may include a protective member thatprotects the light emitting apparatus 10 which functions as the taillamp 1501.

The protective member has a certain degree of strength, and can be madefrom any material as long as it is transparent. The protective membermay be made from polycarbonate or the like. Further, the protectivemember may be made from polycarbonate mixed with furandicarboxylic acidderivative, acrylonitrile derivative, or the like.

The automobile 1500 may include a body 1503 and windows 1502 attachedthereto. The window may be a window for checking the front or rear ofthe automobile, or may a transparent display. The above-described lightemitting apparatus 10, in which the light emitting element 110 caninclude an organic light emitting material such as an organic EL, may beused in the transparent display. In this case, the components such asthe electrodes included in the light emitting apparatus 10 are formed bytransparent members.

Application examples of the light emitting apparatus 10 according to theembodiments described above will be described with reference to FIGS.14A and 14B. The light emitting apparatus 10 is applicable to, forexample, a system that can be worn as a wearable device such as smartglasses, an HMD (Head Mounted Display), smart contact lenses, or thelike. An image capturing display apparatus that is used in such anapplication example includes an image capturing apparatus that canphotoelectrically convert visible light and a light emitting apparatusthat can emit visible light.

FIG. 14A illustrates a pair of glasses 1600 (smart glasses) according toan application example. An image capturing apparatus 1602 such as a CMOSsensor or an SPAD is arranged on the front surface side of a lens 1601of the glasses 1600. Also, the light emitting apparatus 10 describedabove is arranged on the back surface side of the lens 1601.

The pair of glasses 1600 further includes a control apparatus 1603. Thecontrol apparatus 1603 functions as a power supply that supplies powerto the image capturing apparatus 1602 and the light emitting apparatus10 according to the embodiments. The control apparatus 1603 controls theoperation of the image capturing apparatus 1602 and the operation of thelight emitting apparatus 10. An optical system for focusing light to theimage capturing apparatus 1602 is formed on the lens 1601.

FIG. 14B illustrates a pair of glasses 1610 (smart glasses) according toanother application example. The pair of glasses 1610 includes a controlapparatus 1612, and an image capturing apparatus corresponding to theimage capturing apparatus 1602 and the light emitting apparatus 10 areincorporated in the control apparatus 1612. An optical system forprojecting light emitted from the image capturing apparatus and thelight emitting apparatus 10 in the control apparatus 1612 is formed in alens 1611, and an image is projected onto the lens 1611. In addition tofunctioning as a power supply that supplies power to the image capturingapparatus and the light emitting apparatus 10, the control apparatus1612 also controls the operation of the image capturing apparatus andthe operation of the light emitting apparatus 10. The control apparatus1612 may also include a line-of-sight detection unit that detects theline of sight of a wearer.

Infrared light can be used for the line-of-sight detection. An infraredlight emitting unit emits infrared light to the eyeball of a user who isgazing at a displayed image. When the emitted infrared light isreflected by the eyeball and detected by an image capturing unitincluding a light receiving element, a captured image of the eyeball canbe obtained. Image quality degradation is reduced by providing areduction means that reduces the light from the infrared light emittingunit to the display unit in a planar view.

The line of sight of the user to the displayed image is detected fromthe captured image of the eyeball obtained by the image capturingoperation using the infrared light. A known method can be arbitrarilyapplied for the line-of-sight detection using the captured eyeballimage. As an example, a line-of-sight detection method based on Purkinjeimages caused by the reflection of the emitted light on the cornea canbe used.

More specifically, line-of-sight detection processing is performed basedon a pupil-cornea reflection method. The line of sight of the user isdetected by using the pupil-cornea reflection method to calculate aline-of-sight vector representing the direction (rotation angle) of theeyeball based on the image of the pupil and the Purkinje images includedin the captured image of the eyeball.

A light emitting apparatus 10 according to one embodiment of the presentinvention may include an image capturing apparatus including a lightreceiving element, and control a displayed image based on theline-of-sight information of the user obtained from the image capturingapparatus.

More specifically, in the light emitting apparatus 10, a firstfield-of-view region which is gazed at by the user and a secondfield-of-view region other than the first field-of-view region aredetermined based on the line-of-sight information. The firstfield-of-view region and the second field-of-view region may bedetermined by a control apparatus of the light emitting apparatus 10.Alternatively, the first field-of-view region and the secondfield-of-view region may be determined by an external control apparatusand the light emitting apparatus 10 may receive informationcorresponding to this determination. Control can be performed in thedisplay region of the light emitting apparatus 10 so that the displayresolution of the first field-of-view region will be higher than thedisplay resolution of the second field-of-view region. That is, theresolution of the second field-of-view region may be lowered more thanthe resolution of the first field-of-view region.

In addition, the display region includes a first display region and asecond display region different from the first display region, and aregion with a high degree of priority is determined from the firstdisplay region and the second display region of the display region basedon the line-of-sight information. The first display region and thesecond display region may be determined by the control apparatus of thelight emitting apparatus 10. Alternatively, the first display region andthe second display region may be determined by an external controlapparatus and the light emitting apparatus 10 may receive informationcorresponding to this determination. Control may be performed so thatthe resolution of a region with the high degree of priority will be sethigher than the resolution of a region other than the region with thehigh degree of priority. That is, the resolution of a region with arelatively low degree of priority may be set low.

Note that an AI may be used for the determination of the firstfield-of-view region and the region with the high degree of priority.The AI may be a model configured to estimate, from an image of theeyeball, the angle of the line of sight and the distance to an object asthe target of the gaze by using the image of the eyeball and thedirection actually gazed at by the eyeball of the image as the teachingdata. The light emitting apparatus 10, the image capturing apparatus, oran external apparatus may include the AI program. If the AI program isincluded in an external apparatus, information determined by the AIprogram will be transmitted to the light emitting apparatus 10 bycommunication.

In a case in which display control is to be performed based on visualrecognition detection, the light emitting apparatus 10 according to theembodiments can be applied to a pair of smart glasses that furtherincludes an image capturing apparatus configured to capture the outside.The smart glasses can display the captured outside information in realtime.

The present invention is not limited to the above-described embodiments,and various changes and modifications can be made within the spirit andscope of the present invention. Therefore, to apprise the public of thescope of the present invention, the following claims are made.

According to the present invention, it is possible to provide atechnique that suppresses a light emission variation of a light emittingelement while suppressing an increase in circuit scale.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

This application claims the benefit of Japanese Patent Application No.2021-110881, filed Jul. 2, 2021, which is hereby incorporated byreference herein in its entirety.

What is claimed is:
 1. A light emitting apparatus in which a pixel, thatcomprises a current path including a light emitting element, a drivingtransistor configured to supply a current corresponding to a luminancesignal to the light emitting element, and a light emission controltransistor configured to control light emission or non-light emission ofthe light emitting element, is arranged, wherein in the current path,the light emission control transistor is arranged between the lightemitting element and the driving transistor, and a withstand voltage ofthe driving transistor is lower than a withstand voltage of the lightemission control transistor.
 2. The apparatus according to claim 1,further comprising a light emission control circuit configured tosupply, to a control terminal of the light emission control transistor,a light emission control signal for controlling light emission ornon-light emission of the light emitting element, wherein a withstandvoltage of a transistor arranged in the light emission control circuitis lower than the withstand voltage of the light emission controltransistor.
 3. The apparatus according to claim 2, wherein a differencebetween the withstand voltage of the driving transistor and thewithstand voltage of the transistor arranged in the light emissioncontrol circuit is smaller than a difference between the withstandvoltage of the driving transistor and the withstand voltage of the lightemission control transistor.
 4. The apparatus according to claim 3,wherein the withstand voltage of the driving transistor is equal to thewithstand voltage of the transistor arranged in the light emissioncontrol circuit.
 5. The apparatus according to claim 1, wherein thelight emission control transistor comprises a drain offset structure. 6.The apparatus according to claim 1, wherein the light emission controltransistor comprises a LOCOS offset structure.
 7. The apparatusaccording to claim 1, wherein a cascode transistor configured to controla potential of a drain of the driving transistor is further arrangedbetween the driving transistor and the light emission control transistorin the current path, and a withstand voltage of the cascode transistoris lower than the withstand voltage of the light emission controltransistor.
 8. The apparatus according to claim 7, wherein a differencebetween the withstand voltage of the driving transistor and thewithstand voltage of the cascode transistor is smaller than a differencebetween the withstand voltage of the driving transistor and thewithstand voltage of the light emission control transistor.
 9. Theapparatus according to claim 8, wherein the withstand voltage of thedriving transistor is equal to the withstand voltage of the cascodetransistor.
 10. The apparatus according to claim 7, further comprising abias circuit configured to supply a bias signal to a control terminal ofthe cascode transistor, wherein a withstand voltage of a transistorarranged in the bias circuit is lower than the withstand voltage of thelight emission control transistor.
 11. The apparatus according to claim10, wherein a difference between the withstand voltage of the drivingtransistor and the withstand voltage of the transistor arranged in thebias circuit is smaller than a difference between the withstand voltageof the driving transistor and the withstand voltage of the lightemission control transistor.
 12. The apparatus according to claim 11,wherein the withstand voltage of the driving transistor is equal to thewithstand voltage of the transistor arranged in the bias circuit. 13.The apparatus according to claim 1, further comprising a signal outputcircuit configured to supply the luminance signal to a control terminalof the driving transistor, wherein a withstand voltage of a transistorarranged in the signal output circuit is lower than the withstandvoltage of the light emission control transistor.
 14. The apparatusaccording to claim 13, wherein a difference between the withstandvoltage of the driving transistor and the withstand voltage of thetransistor arranged in the signal output circuit is smaller than adifference between the withstand voltage of the driving transistor andthe withstand voltage of the light emission control transistor.
 15. Theapparatus according to claim 14, wherein the withstand voltage of thedriving transistor is equal to the withstand voltage of the transistorarranged in the signal output circuit.
 16. The apparatus according toclaim 1, wherein the withstand voltage of the light emission controltransistor is the highest among the transistors included in theapparatus.
 17. The apparatus according to claim 1, wherein the apparatuscomprises a substrate and a plurality of pixels including the pixel onthe substrate, and the plurality of pixels are arranged along alongitudinal direction of the substrate.
 18. A display apparatuscomprising the light emitting apparatus according to claim 1; and anactive element connected to the light emitting apparatus.
 19. Aphotoelectric conversion apparatus comprising: an optical unitcomprising a plurality of lenses; an image sensor configured to receivelight having passed through the optical unit; and a display unitconfigured to display an image, wherein the display unit displays animage captured by the image sensor, and comprises the light emittingapparatus according to claim
 1. 20. An electric equipment comprising: ahousing provided with a display unit; and a communication unit providedin the housing and configured to communicate with the outside, whereinthe display unit comprises the light emitting apparatus according toclaim
 1. 21. An illumination apparatus comprising a light source and atleast one of a light diffusion unit and an optical film, wherein thelight source comprises the light emitting apparatus according toclaim
 1. 22. A mobile body comprising a body and a lighting unitprovided in the body, wherein the lighting unit comprises the lightemitting apparatus according to claim
 1. 23. A wearable devicecomprising a display apparatus configured to display an image, whereinthe display apparatus comprises the light emitting apparatus accordingto claim
 1. 24. An image forming apparatus comprising: a photosensitivemember; an exposure light source configured to expose the photosensitivemember; a developing device configured to apply a developing agent tothe exposed photosensitive member; and a transfer device configured totransfer an image developed by the developing device to a print medium,wherein the exposure light source comprises the light emitting apparatusaccording to claim 1.